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Diffstat (limited to 'arch/x86/cpu/start16.S')
| -rw-r--r-- | arch/x86/cpu/start16.S | 113 |
1 files changed, 113 insertions, 0 deletions
diff --git a/arch/x86/cpu/start16.S b/arch/x86/cpu/start16.S new file mode 100644 index 0000000000..f1b9d0a0c9 --- /dev/null +++ b/arch/x86/cpu/start16.S @@ -0,0 +1,113 @@ +/* + * U-boot - x86 Startup Code + * + * (C) Copyright 2008-2011 + * Graeme Russ, <graeme.russ@gmail.com> + * + * (C) Copyright 2002,2003 + * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se> + * + * See file CREDITS for list of people who contributed to this + * project. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of + * the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, + * MA 02111-1307 USA + */ + +#include <asm/global_data.h> +#include <asm/processor-flags.h> + +#define BOOT_SEG 0xffff0000 /* linear segment of boot code */ +#define a32 .byte 0x67; +#define o32 .byte 0x66; + +.section .start16, "ax" +.code16 +.globl start16 +start16: + /* Set the Cold Boot / Hard Reset flag */ + movl $GD_FLG_COLD_BOOT, %ebx + + /* + * First we let the BSP do some early initialization + * this code have to map the flash to its final position + */ + jmp board_init16 +.globl board_init16_ret +board_init16_ret: + + /* Turn of cache (this might require a 486-class CPU) */ + movl %cr0, %eax + orl $(X86_CR0_NW & X86_CR0_CD), %eax + movl %eax, %cr0 + wbinvd + + /* load the temporary Global Descriptor Table */ +o32 cs lidt idt_ptr +o32 cs lgdt gdt_ptr + + /* Now, we enter protected mode */ + movl %cr0, %eax + orl $X86_CR0_PE, %eax + movl %eax, %cr0 + + /* Flush the prefetch queue */ + jmp ff +ff: + /* Finally jump to the 32bit initialization code */ + movw $code32start, %ax + movw %ax, %bp +o32 cs ljmp *(%bp) + + /* 48-bit far pointer */ +code32start: + .long _start /* offset */ + .word 0x10 /* segment */ + +idt_ptr: + .word 0 /* limit */ + .long 0 /* base */ + +/* + * The following Global Descriptor Table is just enough to get us into + * 'Flat Protected Mode' - It will be discarded as soon as the final + * GDT is setup in a safe location in RAM + */ +gdt_ptr: + .word 0x20 /* limit (32 bytes = 4 GDT entries) */ + .long BOOT_SEG + gdt /* base */ + + /* The GDT table ... + * + * Selector Type + * 0x00 NULL + * 0x08 Unused + * 0x10 32bit code + * 0x18 32bit data/stack + */ + +gdt: + .word 0, 0, 0, 0 /* NULL */ + .word 0, 0, 0, 0 /* unused */ + + .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ + .word 0 /* base address = 0 */ + .word 0x9B00 /* code read/exec */ + .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ + + .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ + .word 0x0 /* base address = 0 */ + .word 0x9300 /* data read/write */ + .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ |
